The present invention relates to a memory fine tuning arrangement used for television tuners, and more particularly to an improved and simplified fine tuning mechanism used for rotary pre-setting fine tuning devices.
Turret type television tuners generally include an incrementally rotatable channel selector shaft for selectively connecting certain elements of a plurality of tuned circuit elements for each of a plurality of channel selector positions. For example, one such turret tuner arrangement is disclosed in U.S. Pat. No. 4,128,821, wherein a rotatable turret having a plurality of tuning coil units, is rotatably mounted on a chassis base. For clear reception in each of the channel positions of the selector shaft in such tuners, it is customary to include an adjustable impedance device in the local oscillator circuit. This impedance device is conventionally adjusted by means of a fine tuning shaft concentrically mounted with respect to the channel selector shaft. The viewer or user can use the fine tuning shaft to adjust the tuning impedance for each predetermined position of the selector shaft. Various memory fine tuning arrangements have been proposed to maintain individual channel tuning adjustments once they have been established by the user or operator without requiring any further adjustment of the fine tuning shaft of the tuner by the user each time a particular channel is selected. One such arrangement is the push pre-setting type fine tuning device that requires the operator to push in a control knob of the fine tuning shaft while maintaining pressure on the knob to rotate the same to adjust a fine tuning element within the tuner. The other arrangement is a rotary pre-setting type fine tuning devide that requires the operator to only rotate a control knob of the fine tuning shaft for fine tuning adjustment. These devices are particularly useful on turret type television tuners having tuned coil assemblies or units for each channel. These coil units are removably mounted in the rotatable turret structure, and are individually provided with an oscillator coil, the inductance of which may be adjusted by means of an adjustable element which extends into an opening in the end of the coil units adjacent to the oscillator coil.
Because television tuners are made in large volumes and in order to be commercially competitive, it is desirable to provide a low cost pre-setting fine tuning device with a minimum number of parts which may be assembled in an easy and simple manner. The fine tuning device requires a mechanical arrangement to translate the rotary motion of the fine tuning shaft into the rotary motion of the adjustment element, since the fine tuning shaft is laterally offset from the axis of the adjustment element in the individual coil units. Further, engagement of the fine tuning shaft with the adjustment element must terminate automatically when the user releases the fine tuning shaft so that the turret is free to rotate to another channel position. For example, such fine tuning devices are disclosed in U.S. Pat. Nos. 3,316,770; 3,466,549; 4,041,422; 4,128,821; 4,152,682; and 4,253,074 for push pre-setting type memory fine tuners, and in U.S. Pat. Nos. 3,183,726 and 3,898,879 for rotary pre-setting type memory fine tuners.
U.S. patent application Ser. No. 97,847 filed on Nov. 27, 1979, now U.S. Pat. No. 4,311,056, discloses an improved rotary pre-setting fine tuning device including a fine tuning driving member mounted concentrically around the channel selector shaft supported between the front and rear walls of the chassis, a spring member located between the chassis and the fine tuning driving member, an idler member for transmitting fine tuning movement that is rotatably supported in the spring member, and a fine tuning adjustment element movably supported in each end of the respective coil units, wherein the fine tuning driving member comprises a plastic fine tuning shaft, a plastic slide gear, and a slip clutch mounted on the metallic channel selector shaft. The spring member, which biases the slide gear in the thrust direction, supports on its inclined flat surface an idler member for transmitting the fine tuning movement of the fine tuning shaft through the slide gear to a fine tuning adjustment element. The fine tuning shaft is mounted concentrically in the fine tuning driving member and rotatably around the channel selector shaft. The fine tuning driving member is connected with the slide gear by cam means. The slip clutch is mounted within a space between the channel selector shaft and the slide gear at a given position of the selector shaft.
The cam means for connecting the fine tuning shaft and the slide gear comprises a driving cam surface formed by the rear end of the fine tuning shaft and a driven cam surface formed by the front end of the slide gear. The slip clutch formed by a resilient collar of lubricant plastic material is inserted in the space formed by the inside surfaces of both the enlarged or greater diametrical portions of the fine tuning shaft and the slide gear and the outside surface of the channel selector shaft. To insure that a frictional force is applied to the slip clutch, a metal spring may be attached to the resilient collar. The inner surface of the collar is frictionally engaged against the outer surface of the channel selector shaft. Further, the fine tuning shaft and the slip clutch are operatively positioned on the channel selector shaft by using retaining means so that the fine tuning shaft may rotate freely when torque is applied to it while the slip clutch is frictionally rotated by means of the slide gear. The slip clutch is provided with recessed and raised portions on the outer surface of the resilient collar. The slide gear is provided with raised and recessed portions along the axial direction the inner surface of the greater diametrical portion thereof so that both the recessed and raised portions are protected against rotational relative displacement while the frictional rotation of the slide gear and of the slip clutch is permitted.
However, it has been found that undesired friction may be produced in the slip clutch of the fine tuning driving member mentioned above. That is, because the resilient collar of the slip clutch is formed of a plastic material, when the slip clutch is rotated at the time of fine tuning operation, a large quantity of frictional heat is generated by the frictional engagement of the plastic slip clutch against the channel selector shaft formed by a metallic material. The inner surface of the plastic slip clutch will be defaced from fatigue due to such frictional heat, and as a result, the obtainable rotational torque becomes unstable. In anticipation of such unstable rotational torque, a metallic spring with a somewhat larger resiliency may be attached to the slip clutch, but such an arrangement often causes an excessive frictional force caused by the slip clutch rubbing against the channel selector shaft during normal operation. Thus, the rotational torque for the fine tuning shaft becomes too large to give the user a feeling of fine tuning. As another countermeasure for adjusting rotational torque it has also been proposed to use grease between the slip clutch and the channel selector shaft, but controlling the amount of grease used is very difficult, so that the slip clutch tends to become excessively and unfavorably slideable.
In consideration of the above disadvantages in the fine tuning device disclosed in U.S. patent application Ser. No. 97,847, I have found an improved fine tuning driving member wherein a metallic sheet member supported by a plastic collar member is added between the inner surface of the collar member and the outer surface of the metallic channel selector shaft to make a frictional connection by the metal--to--metal engagement.